The present invention relates to a process for preparing L-ascorbic acid (hereinafter, referred to as ASA) from sodium 2-keto-L-gulonate (hereinafter, referred to as Na.2KLG; its free acid, being referred to as 2KLG).
The 2KLG produced by fermentation is usually present in the form of calcium salt in the fermentation broth, which is produced when a calcium salt added to the broth for controlling the pH value during the fermentation process. This calcium salt is usually separated and purified by conversion into alkali metal salts, particularly the sodium salt, which is insoluble in alcohols (See, for instance, Japanese Patent Publication Nos. 34,799/82 and 34,800/82).